The present invention relates to steering column torque sensors.
Power assisted steering is a standard motor vehicle equipment feature. It happens that in order for a typical power steering control system to properly operate, a steering column torque sensor must be included in the system to close the control loop. Torque sensors, such as resistance strip/strain gauge sensors, capacitance sensors, eddy-current sensors, magneto-elastic sensors, and transformer/strain gauge sensors, have been provided to determine the torque on the steering column. However, these sensors lack the sensitivity required for many of the present power steering control systems. Moreover, these sensors are extremely sensitive to changes in temperature and have limited durability.
The present invention has recognized the above-mentioned prior art drawbacks, and has provided the below-disclosed solutions to one or more of the prior art deficiencies. More specifically, the present invention understands that for reliability, durability, and sensitivity reasons, a non-contact torque sensor can be used to measure torque on a rotating shaft.
A sensor for measuring differential angular displacement between a first shaft segment and a second shaft segment includes a first flux shutter that is coupled to the first shaft segment and a second flux shutter that is coupled to the second shaft segment. The second flux shutter is coaxially aligned with the first flux shutter, and the first flux shutter and the second flux shutter form a plurality of openings. The sensor also includes at least one transmitter coil that is energizable to provide a magnetic field around the flux shutters and at least one receiver coil that senses a change in the magnetic flux that reaches the receiver coil when the flux shutters move relative to each other. The sensor outputs a signal representative of the relative angular orientation of the flux shutters.
In a preferred embodiment, a housing surrounds the coils and the flux shutters. Preferably, a torsion bar couples the first shaft and the second shaft. Moreover, the housing defines a vertical axis and the flux shutters are disposed within the housing perpendicular to the axis. In the preferred embodiment, the receiver coil is surrounded by a first flux concentrator and the transmitter coil is surrounded by a second flux concentrator. The sensor further includes at least one reference target coaxially aligned with the flux shutters and at least one reference coil coaxially aligned with the flux shutters. The reference coil and reference target are used to compensate for changes in the sensor caused by temperature changes.
In another aspect of the present invention, a power steering control system includes a microprocessor, a power source, and a steering column differential angle position sensor. The steering column differential angle position sensor is electrically coupled to the microprocessor, electrically coupled to the power source and mechanically coupled to a steering column. The position sensor transmits a signal to the microprocessor that represents an angular displacement between a first flux shutter and a second flux shutter.
In yet another aspect of the present invention, a method for controlling a power steering system includes installing a first flux shutter on a first steering shaft segment and installing a second flux shutter on a second steering shaft segment. In this aspect of the present invention, the method also includes sensing a differential angular position between the first flux shutter and the second flux shutter and generating a signal representing the differential angular position.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: